Researchers have shown for the first time that development of rheumatoid arthritis (RA) entails stimulation of synthesis of a chemokine by thrombin. They further suggest that the expression of the RANTES chemokine’s mRNA occurs by a protease activated receptor-1 (PAR-1) pathway.

PAR-1 and PAR-3 were expressed in isolated synovial fibroblasts from patients with RA. Thrombin stimulated the expression of RANTES mRNA with time, up to 24 hours’ incubation, in fibroblasts which had PAR-1 with or without PAR-3, but not when they expressed PAR-3 only. Transfection of HeLa cells jointly with a RANTES promoter and PAR-1—but not PAR-3—resulted in a dose dependent increase in RANTES mRNA when stimulated with thrombin compared with controls of unstimulated cells transfected with reporter plasmid.

The researchers used cultured human fibroblasts isolated from eight patients with RA. Semi-quantitative reverse transcriptase-polymerase chain reaction was used to measure PAR and RANTES mRNA. Stimulation of expression of RANTES mRNA was measured by transfection of HeLa cells with a PAR-1 or PAR-3 expression vector and a RANTES promoter-luciferase reporter plasmid, followed by challenge with thrombin at different concentrations.

The RANTES chemokine is important in attracting inflammatory cells, and its concentration is raised in the synovial fluid in active RA. Thrombin concentration is also raised. Thrombin splits fibrinogen into fibrin and acts on cell surface receptors, including PAR-1, PAR-3, and PAR-4. PAR-1 is expressed in synovial fluid in RA. The researchers have already shown that thrombin stimulates multiplication of isolated synovial cells.